Artificial respiration of patients is necessary for various medical applications, e.g., during surgical procedures. Respirators are used for the artificial respiration of patients and may additionally also be used as anesthesia apparatuses for anesthesia with an anesthetic reflector and anesthetic dispensing unit. The expiration gas expired by the patient can be reused at least partly in some respirators, i.e., these devices represent a rebreathing system with a breathing air circulating system. A gas delivery means, which sends the breathing air to the patient during the inspiration, is present in the respirator with the breathing air circulating system. The gas delivery means is either switched off or is operated with a very low delivery flow only during and after the expiration.
It is necessary, especially in anesthesia apparatuses, to feed a mixed gas to the inspiration gas. The mixed gas consists, for example, of oxygen and laughing gas. The gases to be mixed, namely, oxygen and laughing gas, are fed separately through shut-off valves to a mixed gas tank. The gases to be mixed, for example, oxygen or laughing gas, are introduced intermittently, such that only one shut-off valve is alternatingly opened. Thus, either, for example, only oxygen or only laughing gas is fed to the mixed gas tank. The mixed gas is released from the mixed gas tank continuously into a breathing air line system, especially into an inspiration gas line. If a gas to be mixed, for example, oxygen, is introduced into the mixed gas tank, the concentration of oxygen increases in the mixed gas tank, because only oxygen is introduced into the mixed gas tank. This also applies analogously if, for example, only laughing gas is introduced into the mixed gas tank. The mixed gas is released from the mixed gas tank continuously. The mixed gas removed from the mixed gas tank is fed to a breathing air line system of a respirator or anesthesia apparatus. Fluctuations in concentration will occur in the mixed gas tank and hence also in the mixed gas, which is fed to the breathing air line system, because of the intermittent dispensing. However, these fluctuations in concentration are not desirable, because the inspiration gas fed to the patient shall have the most uniform concentration possible.
Local fluctuations in concentration may also occur within the mixed gas tank, so that additional fluctuations may likewise also occur in the concentration of the mixed gas fed to the breathing air line system as a result because of a non-optimal mixing of the mixed gas in the mixed gas tank.